Method and arrangement for controlling the temperature of the outstream flow from a heat exchanger and measuring produced heat

ABSTRACT

Process and device for controlling the temperature of an outbound secondary flow in a secondary circuit from a heat exchanger by a primary flow in a primary circuit, via a member that regulates the primary flow, influenced by a control unit. The enthalpy difference between inbound and outbound primary flow to and from the heat exchanger and the secondary flow are determined. The flow in the primary circuit is determined, and the parameters are supplied to the control unit for controlling the member, whereby the primary flow is controlled in dependence of the secondary flow, so that power supplied to the heat exchanger substantially equals the sum of the power needed to raise the temperature of the secondary flow from the initial temperature to the desired outbound temperature; the assumed power requirement for compensating for energy stored in the heat exchanger; and the assumed leak power from the heat exchanger.

[0001] The present invention relates to a method and a device forcontrolling the temperature of at least one outbound secondary flow in asecondary circuit from a heat exchanger through a pi flow in a p acircuit, via a control member which can be affected by a control unit,which member regulates the primary flow. The invention also relates to amethod for measuring yielded power and hea quantity.

BACKGROUND OF THE INVENTION AND THE PROBLEM

[0002] During delivery of hot tap water in district heafing station, apriary flow of centrally heated water, which is conducted into a heatexchanger, where a secondary flow of hot tap water is heated to aconstant consuming temperture in the heat exchanger. Control of theconstant consuming temperature on the secondary side have been obtainedin the district heating station, either through aunomatic mechanical, orthrough electonic control devices, which control the temperature on thebasis of correction of the difference between desired and actualoutbound temperature on the secondary side through feedback tempmaureiasurerent from the secondary side. Whenever electroic control devicesare used, PI or PID regulators are commonly used, which control the flowon the Pnsnar side by, depending on the present outbound temperature onthe secondary side, closing or opening a valve on the primary side.Thus, the heating effect on the pomary side is regulated so that thedesired outbound temperature on the hot tap water is obtained.

[0003] Both to mechanical ad the electronic systems exhibit drawbacks,since the control is not as fast as would be desired, whereby there maybe a delay before the correct outbound temperture is reached on thesecondary side. This entails a lag before the correct temperate isobtained at the tap location of the secondary circuit, and, in the worstcast, a risk of scalding.

[0004] Another drawback is that an osci ation in the control easilyarises, since it is, in practise, impossibly to optimise the regulatingequipment with respect to all occurring operating conditions. Theconducting temperat and difference pressure of the district heatingsystem, i.e., the simary sde, varies during the year and along the pathof the district heating line.

[0005] The pressure fluctuations in the distict heating system arepartly dependent on the present distance from the heat source, partly onthe relative position of the district-heating central in the system. Thestatically programmed characustics of the regulators cannot be optimisedwith respect to all occuring operation scenarios, which entails, amongother things, oscillations of the outbound temperature during certainopening conditions. The temperame oscillations entail e.g. the followingpotential drawbacks.

[0006] Poor comfort at top locations with a small smoothening effectfrom the line system, which I particularly noticeable ir singlehousehold residential property.

[0007] Increased calcification of heat exchangers when tempertures above60° C. are reached. Increased wear of regulating members.

[0008] Impaired cooling of the district heating system, which may entaillarge production costs.

[0009] A system is previously known from U.S. Pat. No. 5,363,905, wherea feedback temperature from the secondary side is used to affect theregulaty valve on the primary side. This type of solution correctsdifferent pressures on thep pmary side, but it does not provide thedesired rapid cormrtion of the tempure during fluctuations in th flow ofhot tap water on the secondary side. In this case, measuring of thepressure drop over a construction in the circuit is used, as well aspressure measurement on the primary side, but also meaument of the tebefore and after the beat exchanger on the primary side. This systembecomes retively expensive, since two pressure gauges arm neded on theside, and can not ready provide rapid regulation of the temperare on thesecondary side upon sudden changes of the tap flow on the secondaryside. The regulatory measures will not come into action until thetemperature actually drops on the secondary side, and the typicaloscillations of the hot tap water temperature are obtained.

[0010] EP 0,526,884 discloses a regulatory technique from thermoprinters, in which the write head is controlled to a constanttemperature, primarily by regulatng the electric energy delivered to theprint head, and secondarily by an adjustably compensating coolant flow.The temperature of the thermal head is measueed by a first temperaturesensor, and the temperature of the removed coolant fluid is measured bya second temperature sensor. The system calculates the removed heatingcapacity in the coolant flow by measuring and regulating the coolantflow, and measures the temperature of the inbound, as well as theoutbound heated), coolant flow.

[0011] Through WO 96/17210, a control system for a district heatingplant is previously known, in which is comprised temperaturemeasurements, and measurement of the flow on the side, with the purposeto provide the desired control, and to calculate the consumed power tobe billed to the customer. Also in this case, flow measurement was notused on the secondary side, meaning that the system likely is subjectedto oscillations in the temperture of the outbound water on the secondaryside.

[0012] DE U 1 296,17,756 discloses a system in which a shunting controlis carried out on the primary side, with a feedback, on the side, ofoutbound flow from the heat exchanger, back to the inbound flow of theheat exchanger. Here, the assumption is made that if the, temperature ofthe outbound flow on the primary side from the heat exchanger is keptcontant, a constant temperature of the hot tap water on the secondaryside will be obtained. This assumption unconditionally entails thatoscillations of the temperature on the secondary side are obtned sincethe surfaces of the heat exchanger first must be cooled by the hot tapwater. Further, the system does not respond rapidly to abrupt increasesin the flow of hot tap water, since the regulation is not effected untilthe temperature on he primary side has dropped.

[0013] The prior art has not recogised the need to take rapid actionwhen the heat consumption on the secondary side abruptly changes, i.e.,when the flow is altered incrementally. This means that the conrmolsystems often end up in oscillating conditions, as far as thetemperature on the secondary side is concerned. In spite of themultitude of separate solutions to the parial problems, no system hasexhibited characteristics, simultaneously allowing a stabile functionregardless to the location in the district heating system. Most systemsin which the temperature is to be carefully controlled on the secondaryside have comprised regulatory loops with feedback informationconcerning the current temperature value of the outbound temperaturefrom the taken against the deviation of the measured value of theoutbound temperature from the desired value of the same. Thus, thissyetem is based on action in dependence on the error in the resultingoutbound temperature. Such a system must wait until an error can bedetected before counternmeasures can be taken, which entails a delay ofthe time point when the actual desired heat consumption is altered.

THE PURPOSE OF THE INVENTION

[0014] The purpose of the invention is to obtain a rapid and stablecontrolling equipment in hea exchanging systems, where large variationsmay occur on the primary side as far as inbound temperatures anddifferental pressure are concerned, where an improved consistency of thehot tap water temperature on the consumer side is achieved without thenecessity for feedback of the actual temperature value from thesecondary side, for actually keeping ete temperature constant.

[0015] These task have been solved thugh the characteristics indicatedin the accompanying claims.

[0016] Through the invention, the risk for oscillations in thetemperature is eliminated on the secondary side, which in a districtheaig plant corresponds to a hot tap water circuit. Often, a districtheating plot also has hew exchange circuits for radiator and ventilationsystems, for which te invention is wall adapted. For this type ofsystems, the dynamics of load changes are often slower.

[0017] The invention provides improved load adaptability, independent ofconsumer size. Also, the risk for calcific in beat exchangers is recicedsignificantly, since faster cool systems with higher Con can countertemp ure peaks above 60° C.

[0018] Consistency of the hot top wat temperature on the consumer sideis based upon determinaion of the needed heating power needed toincrease (alternatively, in a cooling applicaton, to reduce) thetemprature of the secondary flow to a deared value. The invention is notbased upon a dynamic capon of the error between the desired and theacual tehpera of the outbound secondary meum, which entails that thecontrol may be executed without feedback of the actual temperature valuefrom the secondary side.

[0019] In most district heating systems, the invention also entails thatthe control system may be installed without adjustment of regulatoryparameters, which strongly reduces the time required for installationand service/fine tuning.

[0020] In a further embodiment, the procedure and the device aresuitable also to be able to deal with changes on the secondary side,concerning temperature fluctuations of the inbound water to be heated inthe heat exchanger. This embodiment is applied when the temperature ofthe inbound cold water fluctuates. (In the no case, the water is assumedto have a largely constant temperature.) Through this embodiment, thesame system may be applied in a g geographical region, and for anotherregion corrections, mainly for possible temperature fluctuaions of theinbound fresh water, may take place through simple modifications.

[0021] The invention may also be utilised for measuring transmittedpower and heat quantity, e.g. for billing purposes or follow-up ofenergy expenditure, and it is also applicable in cooling applications,whereby only the direction of the heat transport is changed.

DESCRIPTION OF THE DRAWINGS

[0022] Below, the invention wil be fur describe in the for of a numberof embodiments, with reference to the accompanying drawings.

[0023]FIG. 1a, schematically shows a connection diagram of the system ofthe invention.

[0024]FIG. 1b-d, shows examples of vanations of embodiments of thesystem of FIG. 1.

[0025]FIG. 2 shows an example of a vadation of the system with a hot tapwater and Hot-ServiceWater Circulation (HSWC).

[0026]FIG. 3 shows an eagle of a connection diagram of a districtheating plant, including functions for hot tap water control andradiator water control, measurement of heat quantity, error detection,an alarm, with means of communication to a superior system.

[0027]FIG. 4 schematically shows an integed hydraulic unit for thecontrol and measurement of a primary flow according to the invention,including valve member, differential pressure sensor, and temperaturesensor, and a control member acting on the valve meer, which may beintegrated in the hydraulic unit or, alternatively, arranged on thesame.

[0028]FIG. 5 shows a section through an integrated hydraulic unitcomprising several occurring fuctions of the invention, for a heatexchange circuit.

[0029]FIG. 6 shows three heat exchangers, each connected to anintegrated hydraulic unit, interconnected for mutual connection of flowand three separate connections for secondary flows, and a common controlunit.

DESCRIPTION OF EMBODIMENTS

[0030]FIG. 1a shows an impentation of the invenition in a districtheating station of a cousider. The station ompnrises a boat exchanger 1,compnsuig a circuit 3, and a secondary circuit 2. The inbound primaryflow 3i to the circuit 3 is constituted by hot water from the centralheating system, while the outbound primary flow 3u is constitited byrecycled water. The seco flow 2i of the secondary ciit 2 is consti d byincoming fresh water, heated in the heat exchanger 1, while the tappedsecondary flow 2i is constituted by heated hot tap water, conductd tothe taps of the end consumer or the customer. When the temperature ofthe inbound secondary flow 2i can not be assumed to be otherwise known(for instance, tough being constant and known beforehand), a temperaturegauge is arranged in the inbound flow 2i (shown with dashed lines in thefigures).

[0031] A flow meter 4 is arranged in the secondary circuit 2i-2u,preferably on the opening side, and the signals of which the flow meteris directed towards a control unit 7. On the primary side, a firsttemperature gauge 8 is arranged at the inbound flow 3i, and a secondtemperature gauge 9 is arranged at the return flow 3u. The outputsignals from these gauges a transmitted to the control unit 7.

[0032] For the control of the flow 3 through the primary side, a controlvalve 5 is arranged in the primary circuit, preferably on the returnflow 3u, which gives lower temperature and cavitaton loads on the valve.The degree of opening, a, of the valve is regulated by a control member25, which in tumn receives control sials from the control unit 7.

[0033] In the shown embodhient, a pressure diff e gauge 6 is used fordetermination of the flow through the primary circuit 3i-3u, which gaugeis connected between the inlet and outlet of the control valve 5.

[0034]FIG. 1b, an embodiment similar to the one shown in FIG. 1 a isshown, but the control member acting on the primary circuit isconstituted by a pump 11. with a predetermined relation between the flow3 through the same as a function of the rotation speed, and thedifference pressure across the pump. The difference pressure AP acrossthe pump is measured by a pressure difference gauge 6. Th control unit 7controls the rotation speed of the pump to the desired flow 3.

[0035] Another embodient is shown in FIG. 1c, where the control of thedesired flow takes place by neasuring the primary flow 3 with a flowgauge 12, and by regulating the opening degree of the valve, a, to adesired primary flow (N. B., local regulatory loop with feedback of theactual flow value).

[0036] The embodiment of FIG. 1d is a fourth variety, in which the flowmeasurement is effected by mmans of a stationary constricting member 13,and a gauge 6, arranged across it, for measurement of the differencepressure across the constricting member.

[0037]FIG. 2 shows an embodiment, where incoming freshwater 2i on thesecondary side is constituted of a mixture of cold water and recycled,so called HSWC flow of hot water. In this case, a varying temperature ofthe inbound secondary flow 2 is obtained, whereby a temperature gauge 10for measuring this temperature Tsin has to be included.

[0038]FIG. 3 shows an embodiment of the invention in a district heatingstation, where a number of occuring functions have been included. Thefunctions of the example comprises hot tap water control and radiatorwater control, and measurement of total transferred heat tap watercontrol and radiator circuit, as well as presentation of thisinformation via a communication link (com) to an external superiorsystem. Diagnostic functions for the heat exchanger and the othercomponents of the station, implemented by means of measurement valuesoccurring in the system, and communication with the superior central via(com), are contemplated to be part of the function and/or themeasurement of heat quantity (whereby this sensor value is not used inthe dynamic temperature consistancy).

[0039] Basic Theory for the Control

[0040] The invention is based on that the yielded/absorbed power of theprimary circuit is to be controlled towards a currently desiredsupplied/removed power to/form the secondary medium, in order to changethe temperature from the current temperature of the inbound secondaryflow to a desired temperature of the outbound secondary flow. This iscarried out through control of he flow in the primary circuit independence of the difference between the temperatures of the inbound andoutbound primary flows.

[0041] In general, for the and secondary circuits of heat exchangers:

Q′=m*(h(T_(in))−h(T_(out)))   (A)

[0042] Where Q′ correspands to the power transported the circuit to theheat exchanger, m corresponds to the mass flow in the circuit, h(T)corresponds to the enthalpy of the medium (energy per mass unit) attemperature T, T_(out) corresponds to the temperature of the outboundflow, and T_(in) corresponds to the temperature of the inbound flow.

[0043] Equation (A) may be written alternatively as:

Q′=m*C_(p)*ΔT   (A2)

[0044] where C_(p) is the heat capacity of the medium, andΔT=T_(out)−T_(in).

[0045] The desired a supplied to the secondary medium, −Q′_(sek) _(—)_(desired), in order to achieve the desired temperature of the outboundsecondy flow, is governed by the equation:

−Q_(sec) _(—) _(desired)=m_(sec)*(h_(sec) _(—) _(out) _(—)_(desired))−h_(sec)(T_(sec) _(—) _(in)))   (A3)

[0046] where m_(sec) corresponds to the mass flow n the secondarycircuit, h_(sec)(T) corrsponds to the enthalpy of the secondary mediumat temperature T, _(sec) _(—) _(out) _(—) _(desired) corrsponds to thedesired temperature of the outbound secondary flow, and T_(sec) _(—)_(in) corresponds to the current temperature of the inbound secondaryflow.

[0047] During heat exchange, there is a power balance where the sum ofsupplied power via the primary side Q′_(prim), via the secondary sideQ′_(sec), and via any leakage Q′_(leak) to the heat exchanger equals theincrease of the energy stored in the heat exchanger per time unitQ′_(vx), i.e.

Q′_(vx)=Q′_(prim)+Q′_(sec)+Q_(leak)  (B)

[0048] The invention comprises control of the power yielded from theprimary side Q′_(prim), so that:

Q′_(prim)=Q′_(sec) _(—) _(desired)−Q′_(leak)+Q′_(vx)   (B2)

[0049] If the leakage effect is negligible, Q′_(leak) is also set tozero, which gives:

Q′_(prim)=Q′_(sec) _(—) _(desired)+Q′_(vx)  (B3)

[0050] During load changes it may be appropriate to cousider Q′_(vx),which constitute a dynamic effect of changes in stored energy in theheat exchanger. For example, a system may be controlled by means of aregulatory valve with a relatively low speed of adjustment. This will,e.g. in the case of a rapid reduction in load, imply that the primary,circuit delivers more energy than desired, as long as the control memberhas not reached the desired position. The supplied “surplus energy” ispartly stored in the heat exchanger, and will entail a temporaryincrease of the outbound secondary temperature. This increase intemperture maybe minimised by means of that the control is compensatedfor the surplus energy in the heat exchanger by temporarily reducing thesupplied primary power until the surplus energy has been removed by thesecondary flow.

[0051] In stationary condition, the energy stored in the heat exchangeris not altered, i.e., Q′_(vx)=0, which when inserted into equation (B3)gives:

Q′_(prim)=Q′_(s)   (B4)

[0052] Insertion of equation (A) applied to the primary side, and (A3)into equation (B4) yields:

m_(prim-desired*(h)_(prim)(T_(prim-in))−h_(prim)(T_(prim-out)))=m_(sec)*(h_(sec-out-desired))−_(sec)(T_(sec-in)))  (C)

[0053] Elimination of m_(prim-desired) from equation (C) gives the basiccontrol principle of the invention in the form: $\begin{matrix}{m_{prim\_ desired} = {m_{\sec}*\left( \frac{\left. {\left. {{h_{\sec}\left( T_{{sec\_ out}{\_ desired}} \right)} - h_{\sec}} \right)T_{sec\_ in}} \right)}{{h_{prim}\left( T_{prim\_ in} \right)} - {h_{prim}\left( T_{prim\_ out} \right)}} \right)}} & (D)\end{matrix}$

[0054] This basal control principle may be evaluated in different formsand with a differing degree of approximate simplifications, some ofwhich are shown below. Flows are often determined in the form of volumeflows, and it is thus not necessary to recalculate equation (D) forvolume flows. For mass flow, m:

m=q*ρ  (E)

[0055] where q is the volume flow and ρ is the density. Since ρ istemperature dependent, the temperature at which a volume flow isdetermined should often be taken into consideration. Assume that thevolume flow of the secondary side q_(prim) _(—) _(desired) is at theinbound side, and the desired flow of the primary side q_(prim) _(—)_(desired) is determined at the outbound side. After insertion ofequation (E) into equation (D), the equation may be solved for q_(prim)_(—) _(desired). $\begin{matrix}\begin{matrix}{q_{prim\_ desired} = {q_{\sec}*\frac{\rho_{\sec}\left( T_{sec\_ in} \right)}{\rho_{prim}\left( T_{prim\_ out} \right)}*}} \\{\frac{{h_{\sec}\left( T_{{sec\_ out}{\_ desired}} \right)} - {h_{\sec}\left( T_{sec\_ in} \right)}}{{h_{prim}\left( T_{prim\_ in} \right)} - {h_{prim}\left( T_{prim\_ out} \right)}}}\end{matrix} & (F)\end{matrix}$

[0056] If the volume flow is determined elsewhere, equation (E) shouldbe applied at the temperature of the medium at the volume measurementlocation. For the enthalpy h(T):

h(T)=c_(p)*T

[0057] where c_(p) is the heat capacity (energy per unit weight anddegree).

[0058] Insertion of equation (G) into equaton (P) gives: $\begin{matrix}{q_{prim\_ desired} = {q_{\sec}*\frac{\rho_{\sec}}{\rho_{prim}}*\frac{c_{p{(\sec)}}*\Delta \quad T_{sec\_ desired}}{c_{p{({prim})}}*\Delta \quad T_{prim}}}} & ({F2})\end{matrix}$

[0059] where ΔT_(sec) _(—) _(desired)=T_(sec) _(—) _(out) _(—)_(desired)−T_(sec) _(—) _(in)and ΔT_(prim)=T_(prim) _(—) _(in)−T_(prim)_(—) _(out).

[0060] By use of the same media in the primary and secondary circuits,and the temperature dependence of ρ and c_(p) is neglected(ρ_(sec)=ρ_(prim); c_(p(sec))=c_(p(sec))), the equation (F2) may bereduced to: $\begin{matrix}{q_{{prim},{bör}} = {q_{\sec}*\frac{\Delta \quad T_{sec\_ bör}}{\Delta \quad T_{prim}}}} & ({F3})\end{matrix}$

[0061] Thus, the invention may be evaluated according to several more orless approximate methods (e.g., by control accoding to equation D, F, F2or F3). They all have in common that they are based on a parameterarray, characteristic of the enthalpy difference (Δh) between theprimary flow (3i) inbound to the heat exchanger (1) and the secondaryflow (3u) outbound from the heat exchanger (1), e.g a number of pointsfor the function h(T) in the primary medium in a temperature rangecharacteristic for the application, and T_(prim) _(—) _(out), T_(prim)_(—) _(in). An example of an alternative characteristic parameter arrayfor said enthalpy difference is constituted by the heat capacity c_(p)for the primary medium in a temperature range that is relevant for theapplication, and the temperature difference ΔT_(prim).

[0062] Similarly, differmt characteristic parameter arrays for the massflow (m_(sec)) in the secondary circuit (2) and the mass flow (m_(prim))in the primary circuit (3) may be used according to the invention.

[0063] The Consturction of the Regulatory Valve

[0064] The valve 5 may be of different design, with flow characteristicsfor the particular construction known. Examples of valves include seat,sliding, ball or mushroom valves. When using a sliding valve, which isaffected by an opening/closing regulating screw, the magnitude of theopening is substantially proportional to the stroke a.

[0065] For each type of valve, the flow characteristics kv(a) may bedetermined, depending on the current pressure across the valveΔP_(value), the flow through the valve Q_(value), and the degree ofopening a of the valve. Thus, the flow through the valve is determinedby the relationship

q_(ventil)=k_(v)(a)·{square root}{square root over (Δp_(ventil))}  (H)

[0066] from which maybe solved; $\begin{matrix}{{k_{v}(a)} = {\frac{q_{ventil}}{\sqrt{\Delta \quad p_{ventil}}}\quad {and}}} & (I) \\{a = {f_{cv}\left( \frac{q_{ventil}}{\sqrt{\Delta \quad p_{ventil}}} \right)}} & (J)\end{matrix}$

[0067] where f_(cv(x) is the inverse function of K) _(v)(x).

[0068] Control Function on a Valve with Differential PressureMeasurement

[0069] During use of a valve, the position of the valve is controlled sothat a correct flow is obtained. For each type of valve, it is possibleto determine empirically the obtained flow, based on of the currentvalve position and differential pressure across the valve.

[0070] The valve position a, desired for control, may be expressed as afunction of the detected flow of the secondary circuit, the detectedtemperature difference on the primary side, the detected differetialpressure over the regulatory valve, and the desired temperturedifference of the secondary circuit.

[0071] For each desired flow in the primary circuit, control of thevalve position a may be effectuated according to the equation:$\begin{matrix}{a_{desired} = {f_{cv}\left( \frac{q_{prim\_ desired}}{\left. \sqrt{}\left( {\Delta \quad p_{valve}} \right) \right.} \right)}} & ({J2})\end{matrix}$

[0072] which, upon inserton of equation (F) into equation (J2), yields aform of the control aciple of hee invention: $\begin{matrix}\begin{matrix}{a_{desired} = {f_{cv}\left( {\frac{q_{\sec}}{\left. \sqrt{}\left( {\Delta \quad p_{valve}} \right) \right.}*\frac{\rho_{\sec}\left( T_{sec\_ in} \right)}{\rho_{prim}\left( T_{prim\_ ut} \right)}*} \right.}} \\{\frac{{h_{\sec}\left( T_{{sec\_ ut}{\_ desired}} \right)} - {h_{\sec}\left( T_{sec\_ in} \right)}}{{h_{prim}\left( T_{prim\_ in} \right)} - {h_{prim}\left( T_{prim\_ out} \right)}}}\end{matrix} & (K)\end{matrix}$

[0073] or, upon insertion of (F3) into (J2): $\begin{matrix}{a_{bör} = {f_{cv}\left( {\frac{q_{sck}}{\sqrt{\Delta \quad p_{ventl}}}*\frac{\Delta \quad T_{sek\_ bör}}{\Delta \quad T_{prim}}} \right)}} & ({K2})\end{matrix}$

[0074] since the same heat carrier is used on the primary and secondarysides, and since the temperature dependence of p and c_(p) is neglected.For each valve, current inverse flow characteristics fcv(x) (and/or itsflow characteristics hv(x)) may be empirically determined.

[0075] Determination of the differential pressure ΔP_(value) iscontemplated to be able to be performed in an arbitrary way, forexample, by means of a pressure difference gauge connected upstream anddownstream of the valve, or by means of a first absolute pressure gaugefor measuring the pressure P1 upstream of the valve and another absolutepressure gauge for measuring the pressure P2 downstream of the valve.

[0076] Measurement of Power and Heat Quantity

[0077] Measurement of supplied effect and heat quantity may be conductedon the primary side and/or the secondary side of a heat exchanger, basedon equation (A). Equations (H) and (E), applied to the medium in thevalve, inserted into equation (A) gives:

Q′_(prim)=ρ_(prim)(T_(prim) _(—) _(valve))*k_(v){squareroot}(ΔP_(valve))*(h(T_(prim) _(—) _(in))−H(T_(prim) _(—) _(out))   (L)

[0078] where T_(prim) _(—) _(valve) is the temperature of the primarymedium in the valve. If the valve is placed in the outbound primary flow(3u) from the heat exchanger, T_(prim) _(—) _(valve) ≅T_(prim) _(—)_(out) , and, respectively, if it is placed in the inbound primary flow(3i) to the heat exchanger, T_(prim) _(—) _(valve)≅T_(prim) _(—) _(in).

[0079] After insertion of equation (G) into equation (L), thealternative equation

Q′_(prim)=ρ_(prim)(T_(prim) _(—) _(valve))*k_(v)(a)*{squareroot}(Δp_(valve)*c) _(p)*Δt_(prim)  (L2)

[0080] is obtained.

[0081] According to a preferred embodiment of the invention, the powersupplied at the primary side is governed partly through determination ofthe temperature T_(prim) _(—) _(in), T_(prim) _(—) _(out), and thedifferential pressure ΔP_(valve) over a regulatory valve placeddownstream of the outlet of the primary side; and partly throughknowledge of the characteristics of the valve k_(v)(a) and thepercentage opening a, and the density and enthalpy of the primarymedium, which values are used for the calculation of Q′_(prim) accordingto equation (L), alternatively (L2).

[0082] By integrating the effect yielded during a period of time t1-t2,the heat quantity supplied by the primary circuit during this period isobtained. $\begin{matrix}{Q_{prim} = {\int_{t1}^{t2}{\left( Q_{prim}^{\prime} \right){\partial t}}}} & (M)\end{matrix}$

[0083] Equation (L) inserted into equation (M) yields: $\begin{matrix}{Q_{prim}{\int_{t1}^{t2}\left( {{\rho_{prim}\left( T_{prim\_ valve} \right)}*{k_{v}(a)}*\left. \sqrt{}{*\left( {\Delta \quad p_{valve}} \right)*\left( {h\left( {T_{{{prim\_ in})} - h}\left( T_{prim\_ out} \right)} \right)} \right){\partial t}} \right.} \right.}} & ({M2})\end{matrix}$

[0084] The integration may be carried out, e.g., by determination andsummation of partial energies one by one, which energies are determinedas products of periodical average power values Q_(prim) _(—) _(i) andthe corresponding time periods for the formation of the average value ofΔ_(ti): $\begin{matrix}{Q_{prim} = {\sum\limits_{i = 1}^{n}\left( \overset{\_}{Q_{prim\_ i}*\Delta \quad t_{i}} \right)}} & ({M3})\end{matrix}$

[0085] According to a preferred embodiment of the invention, yieldedpower and heat quantity is determined also on the secondary side. Here,the determination is based on the temperatures T_(sec) _(—) _(in) andT_(sec) _(—) _(out), (measured by a fourth temperature gauge) and a flowvalue q_(sec), (measured by a flow gauge or determined in some otherway, e.g., through a rpm-controlled pump with known characteristics) andon equation (A).

[0086] If a stationary state is assumed and heat leakage from the heatexchanger is neglected, the value of the yielded effect and heatquantity on the primary side constitues a first measure, and the valueof yielded effect and heat quantity on the secondary side constitues asecond measure of the power Q′ and the heat quantity Q that has beentransferred in the heat exchanger. Either one of these two independentlydetermined measures of yielded effect and heat quality may be utilisede.g. for billing or follow-up of energy expenditure.

[0087] By comparison of these two independently determined measures, thesecurity of the system can be increased. For example, the redundantvalues of Q′ may be used in order to generate an alarm when the measuresare not reliable if said measures deviate from each other by more than agiven acceptable value of, say, ±10%, or preferably ±2%, of the highervalue.

[0088] A second area of utlisation could be to, based on thedetermination of Q′ through either of the methods, switch the systeminto reserve mode, provided that an error in a measurement signal, whichis included in determination of Q′ according to the other method, wasdetected in a different independent manner. Example: if it isdetermined, e.g., through a reasonability check, that a temperaturegauge on the primary side is out of order, it is possible to determine areserve value for the broken gauge by using a value of Q′ determined onthe secondary side. In similar manner, reserve values may be calculatedfor any gauge, for which error has been detected through an independentmethod.

[0089] A third use could be to self calibrate a gauge or e.g. the valvecharacteristics in the same way used to calculate spare values in thecase of a faulty gauge.

[0090] Integrated Valve Units

[0091] In order to simplify manufacture and assembly of systemsaccording to the invention, several functions may in a preferredembodiment be brought together into an intergrated valve unit, which maybe produced as a semi-manufacturer for subsequent assembly into acomplete system. FIG. 4 schematically shows an intergrated hydraulicunit for the control and measurement of a primary flow according to theinvention, including valve member, differential pressure sensor, andtemperature sensor, and a control member acting on the valve member,which may be integrated in the hydraulic unit or, alternatively,arranged on the same. This hydraulic unit may advantageously by used tocontrol the primary flow and measure the differential pressure acrossvalve members, and the temperature of the primary flow at the valve.

[0092] Several functions/components may be integrated into a hydraulicunit 40, shown in FIG. 5, comprising a first channel 56 between the pipejoints 41 and 42 for connection to the district heating system and theheat exchanger, respectively, and branches 43 and 44 to any adjacentfurther hydraulic units; see FIG. 6.

[0093] In the channel 56, a valve member 53 is arranged on both sides ofthe valve member 53 for measuring the pressure difference upstream anddowmstream of the valve member. Gauges 8 are also arranged in thechannel 56 in order to determine the temperature of the medium in thechannel 56. A second channel 57 is arranged in the hydralic unit 40,which channel may be connected via the pipe joints 45 and 46 to theinbound medium of the district heating system, and to the heatexchanger, respectively. Branchings 47, 48 from the second channel 57may possible be utilised for connecting to adjacent further hydraulicunits. Gauges 9 are also arranged in the other channel 57 in order todetermine the temperature of the medium in this channel. A third andfourth channel 58 and 59 are also part of the hydraulic unit 40, withpipe joints 49 and 51 for connection to the heat/cooling consumer, andpipe joints 50 and 52 towards the heat exchanger. In order to determinethe temperature of the medium in the channels 58 and 59, gauges 55 and10 are arranged in the respective channel. In order to determine theflow of the medium in the channel 59, a gauge 70 is arranged. Contactmembers (not shown) for connection of power lines to and from thehydraulic unit 40 are provided, which transfer measurement and/orcontrol signals.

[0094] The integrated hydraulic hydraulic unit in FIG. 4 may be producedadvantageously in the form of semi manufacture for subsequent assemblyinto a complete system, for example as shown in FIG. 6. The hydraulicunits entail potential advantages in addition to those alreadymentioned, through the considerable simplification of the lying down andconnection of primary and secondary circuits.

[0095] Further Embodiments

[0096] In the most common embodiment, the outbound temperature from theheat exchanger 1 of the secondary flow 2 is constant, e.g., 55° C. Ofcourse, this could also be a manually or automatically adjustabledesired value. The control unit 7 may obtain an adjustment of thedesired valve, for example by a potentiometer. A certain manualadjustment may take place, depending on desires of hot water consumers,or adjusted to the current season of the year. For example, duringwinter, there may be demand for a slightly warmer hot tap water in orderto compensate for heat loss between outbound temperature on thesecondary side may also be effected automatically in the control unitaccording to a predetermined compensation curve and/or a signal from anexternal temperature gauge.

[0097] In one application of the invention in a system where the heatexchanger is to heat a radiator circuit, corresponding correction isneeded in most cases, depending on the outside temperature, as well ascorrection of the temperature of the inbound secondary flow. In thisimplementation, too, there is no need for a direct feedback of thetemperature of the outbound flow on the primary side.

[0098] The control member for the regulatory valve may be severaldifferent kinds, for the heat exchanger. In those embodiments where thedifferential pressure across the valve is measured, an initial cloggingon the primary side (caused by calcium deposits, dirt etc.) may bedetected by analysis of the pressure drop with time for a given openingdegree of the valve. During initial clogging, the pressure drop withtime for a given opening valve drops for a constant flow, since anever-increasing pressure drop will be absorbed by the heat exchanger.Evaluating changes in the heat tranfer of the heat exchanger may alsoperform the diagnostics. For example, the following procedure may beapplied: All measured signals (at least the temperature difference inthe primary circuit, primary flow, secondary flow and the desiredtemperature difference on the secondary side) are saved for a number ofdifferent load conditions (transferred power) and system conditions(inbound primary temperature and pressure). Upon clogging of the heatexchanger, the heat transfer characteristics deteriorate, which entailsa demand for increasing primary flows.

[0099] The wanted difference temperature ΔT_(prim) may be calculatedbase on T_(prim(in)) and T_(prim(out)), or directly measured as atemperature difference, e.g., with a thermo element.

[0100] Since the system contains flow measurement as well as differencetemperature, a calculation of consumed heat quantity for billing of theend consumer may be easily introduced.

[0101] Further, the system is well suited for reading (calculation ofheat transfer), diagnosis (clogging), climate control (centraladjustment of desired values), and a possible switch off function. Onlya single interface to a communications link is needed, which interfaceis connected to the control or regulatory unit.

[0102] The invention is not limited to use in district heating stations;it may be used in all applications of which heat exchangers are a part,for example, in the petrochemical industry or other forms of heatcontrol.

1. A procedure for controlling the temperature of at least one outboundsecondary flow (2u) in a secondary circuit from a heat exchanger (1) bymeans of a primary flow (3) in a primary circuit, where a control unit(7) controls a regulatory member (5, 11) that regulates the primaryflow, characterised in that a) a parameter array, characteristic of theenthalpy difference (Δh) between the inbound primary flow (3i) to theheat exchanger (1) and the outbound primary flow (3u) from the heatexchanger (1), is determined, b) a parameter array, charateristic of themass flow (m_(sec)) in the secondary circuit (2), is determined, c) aparameter array, characteristic of the mass flow(m_(prim) in the primary circuit (3), is determined,) d) and that theparameters determined in points a) through c) are transmitted to thecontrol unit (7) for controlling the regulatory member (5, 11), wherebythe primary flow (3) is controlled in dependence of the secondary flow(2), so that the power transferred to the heat exchanger by the primaryflow (3) substantially corresponds to the sum of: 1) the power needed toraise the temperature of the secondary medium from the current inboundtemperature T_(sec) _(—) _(in) to the desired outbound temperatureT_(sec) _(—) _(out) _(—) _(desired) and 2) assumed power demand forcompensation of stored energy in the heat exchanger (1), and 3) assumedleak power from the heat exchanger.
 2. A procedure according to claim 1,characterised in that, control of the regulatory member occurs throughflow balancing of the primary flow (3) against the secondary flow (2) insuch a way that a power balance is maintained between the primary flow(3) and the secondary flow, where the supplied and consumed power in therespective flow circuit is given by: Q=p.c_(p).q.ΔT, from which powerbalance is given to the flow on the primary side q_(prim) is obtainedthrough control of the control member in such a way that$q_{prim} = {\cdot q_{sek} \cdot \left( \frac{{\rho_{sek} \cdot c_{P_{sek}} \cdot \Delta}\quad T_{sek}}{{\rho_{prim} \cdot c_{P_{prim}} \cdot \Delta}\quad T_{prim}} \right)}$

p_(sec/prim)=predetermined density of the medium in the secondary andthe primary circuit, respectively, c_(psec/prim)=predetermined specificheat of the medium in the secondary and the primary circuit,respectively, Q_(prim)=the flow in the primary circuit obtained from thecontrol member q_(sec)=actual measured flow in the secondary circuitΔT_(prim)=measured temperature difference between the inbound andoutbound media on the primary side, and ΔT_(sec) is the desiredtemperature difference between the inbound and outbound media of thesecondary side, the temperature on the outbound side of the secondarycircuit only being a desired value, whereby the control of theregulatory member is effected without direct feedback of the temperatureof the outbound side of the secondary circuit.
 3. A procedure accordingto claim 1 or 2, characterised in that the regulatory member (5) isconstituted by a regulatory valve with known flow characteristics and bya pressure difference (pressure drop) across the regulatory valvedetermined by a difference pressure gauge (6).
 4. A procedure accordingto claim 3, characterised in that, the degree of opening (a) of thevalve is a function of the preferably empirically determined inverseflow characteristics f_(cv)(x) of the valve according to: whereΔ_(valve) is the measured differential pressure across the regulatoryvalve and q_(prim) _(—) _(desired) is the flow through the valve, and ais the degree of opening of the valve.
 5. A procedure according toclaims 1 or 2, characterised in that, the regulatory member isconstituted by a pump (11) with a predetermined relationship between theflow through the same as a function of the rotational speed anddifferential pressure across the pump, whereby the control unit (7)regulates the rotational speed of the pump.
 6. A procedure according toany of the preceding claims, characterised in that, the temperature(T_(sec) _(—) _(in) of the inbound secondary flow (2i) to the heatexchanger is detected (10), which detected value is used for calculationof q_(prim) _(—) _(desired) .
 7. A procedure according to any of theperceding claims, characterised in that, the flow and temperature valuesin the primary and secondary circuits are used for diagnosing anddetecting clogging of heat exchangers and/or impaired heat transfervalue for the heat exchanger.
 8. A procedure for controlling thetemperature of at least one outbound secondary flow (2) from a heatexchanger (1) in a secondary circuit by means of a primary flow (3) in aprimary circuit passing through the heat exchanger, where a control unit(7) controls a regulatory member (5, 11) arranged to regulate theprimary flow, characterised in that temperature gauges (8, 9) arearranged to measure the temperature of the primary flows inbound to (3i)and outbound from (3u) the heat exchanger (1) for determining teenthalpy difference between these flows, a flow gauge (4) is arranged tomeasure the flow (q_(sec)) of the secondary medium (2), differencepressure gauges (6) are arranged to measure the pressure difference (ΔP)im the primary medium (3i) across the regulatory member (5), and/or thata flow gauge (12) is arranged to measure the flow (q_(prim)) of themedium (3), and that and that the output signals from said gauges(4,8,9,12) are arranged to be transmitted to tlae control unit (7) forcontrolling the regulatory member (5, 11), whereby the primary flow (3)is arranged to be controlled in dependence of the secondary flow (2), sothat the power transferred to the heat exchanger through the primaryflow (3) substantially corresponds to the sum of: 1) the power needed toraise the temperature of the secondary medium from the current inboundtemperature T_(sec) _(—) _(in) to the desired outbound temperatureT_(sec) _(—) out _(—) _(desired) and 2) assumed power demd forcompensation of stored energy in the heat exchanger (1), and 3) assumedleak power from the heat exchanger.
 9. A device according to claim 8,characterised in that, the relgulatory member (5) is constituted by aregulatory valve of known flow dharactertics, a differential press=gauge(6) is arranged to measure the differential pressure a=oss the valve,and by known flow characteristics for the valve (5) stored m the memoryof the control unit (7).
 10. A device accrding to claim
 8. characterisedin that, the regular member is constituted by a pump (11) with apredetermined relationship between the flow through the same as afunction of the rotational speed and differential pressure across thepump, whereby tihe control unit (7) is arranged to regulate the rotationspeed of the pump.
 11. A device according to claim 8, characterised inthat, the valve (5) is integrated into a hydraulic unit (20) comprisinga valve member (24) with a control memeber (25) actual on the same, pipejoints (22, 23) connected to the valve (5), a device for determining thedifferential pressure (6) across the valve member, which is connectedupstream amd downstream of the valve member (24), a temperature gauge(8) detecting the temperature of the flow through the valve.
 12. Adevice according to any of claim 8-11, characterisied in that, thecontrol unit (7) at least one memory (30) for storing the degree ofopening (a) of the valve (5) as a function of the flow q_(sec) of thesecondary circuit (2), the differential temperature ΔT_(sec) in tesecondary circuit (2), the differential temperature ΔT_(prim) in theprimary circuit (3), and the differential pressure ΔP_(valve) across thevalve (5).
 13. A device according to claim 8, characterised in that,channels (56-59) for conducting medium (3i, 3u, 2i, 2u) to and from theheat exchanger (1) are integrated into a hydraulic unit, that thechannels at ther ends are equipped with pipe joints (41, 42, 45, 46, 49,50, 51, 52) for connection to priamy and secondary flow (3, 2), thatlateral channels (43, 44, 47, 48) are disbranched from at least some ofthe channels, which lateral channels similarly are provided with pipejoints at their ends for connection of connecting lines between severalconnected hydraulic units, and that channel parts for flow, differentialpressure and temperature gauges (8, 9, 10, 55, 61, 62) communicatingwith the channels and at least one regulatory valve are arranged in thehydraulic unit.
 14. A procedure for determining the power and heatquantity transferred to a heat exchanger via the primary circuit of theheat exchanger by means of a regulatory member (5.11), regulating theflow through the primary circuit, which member (5, 11) is effectible bythe control unit (7), characterised in that, the endalpy difference (Δh)between the prinary flow inbound to (3i) and outbound from (3u) te heatexacanger (1) is determined, that the pressure difference(Δp_(regulatory) _(—) _(member)) across, and the medium temperature(T_(medium)) in, the regulatory member (5, 11) with known flowcharacteristics stored in the memory of the control unit (7) aredetermined, that the density of the medium is stored in the memory ofthe control unit (7), that the enthalpy difference (Δh), the pressuredifference (Δp_(regulatory) _(—) _(member)), the temperature(T_(medium)) and the degree of opening (a) of the regulatory member areregistered, which parameters together with the flow characteristics andthe density stored in the memory of the control unit, provide a value ofthe power and heat quantity yielded by the primary circuit.
 15. Aprocedure according to claim 14, characterised in that, that thedetermined value of the power and heat quantity yielded by the primarycircuit ame checked against simultaneously valid value of the power andheat quantity absorbed by the secondary circuit, which are calculatedfrom the parameters enthalpy difference Δh_(sec) between inbound andoutbound secondary flow and flow m_(sec), which are stored or determinedin the control unit, whereby an alarm is provided to the environment viacommunication means if the values for power and heat quantity yieldedand absorbed by the primary and secondary circuit, respectively, deviatefrom one another by more than a predetermined acceptable value.